Tecnologia verde para estabilização termo-oxidativa de isoladores de silicone

Abstract

Silicone rubber (SIR) is used in the manufacture of insulators for transmitting electrical energy. The addition of some additives can efficiently improve the resistance to thermal degradation of SIR. In this work, an additive based on the Zn(II)-Curcumin complex was developed and studied as a thermal stabilizer of silicone rubber. The Zn(II)-Curcumin complex was synthesized from the reaction of curcumin with zinc sulfate (ZnSO4.7H20), in a molar ratio of 1:1 in methanol solution, kept at reflux for 2 hours. The metal complex was incorporated into silicone rubber in compositions of 2%, 4%, 6%, 8% and 10% by weight. Spectroscopic analyzes confirmed the synthesis of the Zn(II)-Curcumin complex. UV-Vis showed ππ* and nπ* electronic transitions at 435 nm and 450 nm, respectively. Fourier Transform Infrared Spectroscopy (FTIR) showed the disappearance of the bands of the groups (C=O) at 1743 cm-1 and C(O)-C at 1367 cm-1, in the Zn(II)-Curcumin complex. X-ray diffraction (XRD) showed that both curcumin and the complex are crystalline materials and allowed the average crystal size to be determined using the Debye-Scherrer’s Equation. Energy Dispersive Scanning Electron Microscopy (SEM-EDS) analysis showed a different morphology in the metallic complex (irregular aggregates and high porosity). The silicone rubber compositions containing the metal complex (Zn(II)-Curcumin/SIR) were characterized by gel content, contact angle, FTIR, SEM-EDS, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and inductive oxidation time (OIT). The gel content of the Zn(II)-Curcumin/SIR compositions showed that the addition of the complex does not significantly change the degree of crosslinking of the rubber. An increase in the degree of hydrophobicity was observed with the incorporation of the metal complex into the rubber matrix. FTIR confirmed the incorporation of the Zn(II)-Curcumin complex into the rubber. The TGA analysis showed that the incorporation of the metal complex does not change the degradation profile of the SIR, observing a significant increase in the thermal stability of the SIR for concentrations of the metal complex above 8% by weight. The dynamic study of the curing reaction by DSC showed that the incorporation of the Zn(II)-Curcumin complex does not affect the curing reaction.